Sampler : Add visitPixels

include/GafferImage/Sampler.h

@@ -95,6 +95,13 @@ class GAFFERIMAGE_API Sampler
 		/// 0.5, 0.5.
 		float sample( float x, float y );
 
+		/// Call a functor for all pixels in the region.
+		/// The signature of the functor must be `F( float value, int x, int y )`.
+		/// The order is not necessarily scanline order, but it is guaranteed to be
+		/// deterministic and visit every pixel exactly once.
+		template<typename F>
+		void visitPixels( Imath::Box2i region, F &&lambda );
+
 		/// Appends a hash that represent all the pixel
 		/// values within the requested sample area.
 		void hash( IECore::MurmurHash &h ) const;

include/GafferImage/Sampler.inl

@@ -94,6 +94,103 @@ inline float Sampler::sample( float x, float y )
 	return OIIO::bilerp( x0y0, x1y0, x0y1, x1y1, xf, yf );
 }
 
+template<typename F>
+void Sampler::visitPixels( Imath::Box2i region, F &&visitor )
+{
+	if( !BufferAlgo::contains( m_dataWindow, region ) )
+	{
+		if( m_boundingMode == Black )
+		{
+			for( int y = region.min.y; y < region.max.y; y++ )
+			{
+				if( y < m_dataWindow.min.y || y >= m_dataWindow.max.y )
+				{
+					for( int x = region.min.x; x < region.max.x; x++ )
+					{
+						visitor( 0.0f, x, y );
+					}
+				}
+				else
+				{
+					for( int x = region.min.x; x < m_dataWindow.min.x; x++ )
+					{
+						visitor( 0.0f, x, y );
+					}
+
+					for( int x = m_dataWindow.max.x + 1; x < region.max.x; x++ )
+					{
+						visitor( 0.0f, x, y );
+					}
+				}
+			}
+		}
+		else
+		{
+			// If we wanted to optimize this case, we could break the area within
+			// `region` but outside `m_dataWindow` into 8 octants, based on where we reuse
+			// the same border values for multiple outside pixels.  Would be a potentially
+			// huge win for large regions with small data windows, but that's a rare case,
+			// and it would take about 90 lines of fairly fiddly code, it's simpler to do
+			// something slow instead.
+			for( int y = region.min.y; y < region.max.y; y++ )
+			{
+				if( y < m_dataWindow.min.y || y >= m_dataWindow.max.y )
+				{
+					for( int x = region.min.x; x < region.max.x; x++ )
+					{
+						visitor( sample( x, y ), x, y );
+					}
+				}
+				else
+				{
+					for( int x = region.min.x; x < m_dataWindow.min.x; x++ )
+					{
+						visitor( sample( x, y ), x, y );
+					}
+
+					for( int x = m_dataWindow.max.x + 1; x < region.max.x; x++ )
+					{
+						visitor( sample( x, y ), x, y );
+					}
+				}
+			}
+		}
+
+		region = BufferAlgo::intersection( m_dataWindow, region );
+	}
+
+	Imath::V2i minTile = ImagePlug::tileIndex( region.min );
+	Imath::V2i maxTile = ImagePlug::tileIndex( region.max - Imath::V2i( 1 ) );
+	for( int tx = minTile.x; tx <= maxTile.x; tx++ )
+	{
+		for( int ty = minTile.y; ty <= maxTile.y; ty++ )
+		{
+			Imath::V2i tileOrigin = Imath::V2i( tx * ImagePlug::tileSize(), ty * ImagePlug::tileSize() );
+
+			const float *tileData;
+			Imath::V2i tileIndex;
+			cachedData( tileOrigin, tileData, tileIndex );
+			for(
+				int y = std::max( tileOrigin.y, region.min.y );
+				y < std::min( tileOrigin.y + ImagePlug::tileSize(), region.max.y );
+				y++
+			)
+			{
+				for(
+					int x = std::max( tileOrigin.x, region.min.x );
+					x < std::min( tileOrigin.x + ImagePlug::tileSize(), region.max.x );
+					x++
+				)
+				{
+					visitor( *(tileData + ( y - tileOrigin.y ) * ImagePlug::tileSize() + x - tileOrigin.x), x, y );
+				}
+			}
+		}
+	}
+}
+
+
+
 inline void Sampler::cachedData( Imath::V2i p, const float *& tileData, Imath::V2i &tilePixelIndex )
 {
 	// Get the smart pointer to the tile we want.